Spatio-temporal drivers of soil and ecosystem carbon fluxes at field scale in an upland grassland in Germany

Ecosystem carbon (C) fluxes in terrestrial ecosystems are affected by varying environmental conditions (e.g. soil heterogeneity and the weather) and land management. However, the interactions between soil respiration (Rs) and net ecosystem exchange (NEE) and their spatio-temporal dependence on environmental conditions and land management at field scale is not well understood. We performed repeated C flux measurement at 21 sites during the 2013 growing season in a temperate upland grassland in Germany, which was fertilized and cut three times according to the agricultural practice typical of the region. Repeated measurements included determination of NEE, Rs, leaf area index (LAI), meteorological conditions as well as physical and chemical soil properties. Temporal variability of Rs was controlled by air temperature, while LAI influenced the temporal variability of NEE. The three grass cuts reduced LAI and affected NEE markedly. More than 50% of NEE variability was explained by defoliation at field scale. Additionally, soil heterogeneity affected NEE, but to a lower extent (>30%), while Rs remained unaffected. We conclude that grassland management (i.e. repeated defoliation) and soil heterogeneity affects the spatio-temporal variability of NEE at field scale

Soil carbon sequestration due to post‐Soviet cropland abandonment: estimates from a large‐scale soil organic carbon field inventory

The break-up of the Soviet Union in 1991 triggered cropland abandonment on a continental scale, which in turn ledto carbon accumulation on abandoned land across Eurasia. Previous studies have estimated carbon accumulationrates across Russia based on large-scale modelling. Studies that assess carbon sequestration on abandoned land basedon robust field sampling are rare. We investigated soil organic carbon (SOC) stocks using a randomized samplingdesign along a climatic gradient from forest steppe to Sub-Taiga in Western Siberia (Tyumen Province). In total, SOCcontents were sampled on 470 plots across different soil and land-use types. The effect of land use on changes in SOCstock was evaluated, and carbon sequestration rates were calculated for different age stages of abandoned cropland.While land-use type had an effect on carbon accumulation in the topsoil (0–5 cm), no independent land-use effectswere found for deeper SOC stocks. Topsoil carbon stocks of grasslands and forests were significantly higher thanthose of soils managed for crops and under abandoned cropland. SOC increased significantly with time sinceabandonment. The average carbon sequestration rate for soils of abandoned cropland was 0.66 Mg C ha1yr1(1–20 years old, 0–5 cm soil depth), which is at the lower end of published estimates for Russia and Siberia. Therewas a tendency towards SOC saturation on abandoned land as sequestration rates were much higher for recentlyabandoned (1–10 years old, 1.04 Mg C ha1yr1) compared to earlier abandoned crop fields (11–20 years old,0.26 Mg C ha1yr1). Our study confirms the global significance of abandoned cropland in Russia for carbonsequestration. Our findings also suggest that robust regional surveys based on a large number of samples advancemodel-based continent-wide SOC prediction